The present invention relates to systems for controlling and retaining tension in a mesh reflector in the deployed condition, as well as for managing the mesh during launch and transport in the stowed condition.
Dish shaped mesh reflectors are used in various communication systems today, particularly on satellites in orbit around the Earth. Various systems are known for tensioning the various components of a mesh reflector as it is being made and assembled, and for managing the mesh during transport and launch. The known methods for tensioning the mesh reflectors, however, and for retaining the tension in the stowed and launch stages, are relatively costly and involve the use of unnecessary weight. For satellites in particular, any savings in cost and weight can be very significant.
Known mesh tensioning systems use rigid or semi-rigid edge strips along the outer edges (catenaries) of the mesh and often along the gore seams to lock-in tension in the mesh from the time the mesh is laid out until it is installed on a foldable reflector structure. Known systems for retention of the mesh typically use flat straps tensioned by metallic helical springs located behind the mesh.
Known mesh management systems are typically either containment or control systems. In the first category, the mesh is confined to a certain volume and limited in movement within that volume by friction as the layers of the mesh are compressed together. The second category uses positive means to control the location of the mesh prior to deployment and is more reliable.
Known methods, apparatuses, and systems for mesh integration and tension control, mesh retention, and mesh management, add additional weight and cost to the spacecraft and satellite. Although such systems are known to work relatively satisfactory, they may increase thermal distortion and make the adjustment of the mesh surface shape more difficult.
It is an object of the present invention to provide improved methods, apparatuses, and systems for mesh integration and tension control, mesh retention, and mesh management for mesh-type reflectors, particularly for use in satellites. It is also an object of the present invention to reduce the weight and expense of the tensioning, retention, and management systems for mesh reflectors.
It is another object of the present invention to avoid the use of semi-rigid and rigid strips on the mesh during manufacture and assembly, particularly to save weight and cost, enhance reflector transparency, and eliminate mesh stiffening. It is a still further object of the present invention to enhance thermal stability and mesh shape adjustability of a mesh reflector.
It is an additional object of the present invention to provide a more accurate and direct tensioning control system for a mesh reflector while at the same time reducing weight and solar blockage by eliminating straps and metallic springs used in prior art systems. It is also an additional object of the present invention to provide a mesh retention system which utilizes small bending springs located at chord intersections.
It is still a further object of the present invention to provide a mesh management system that provides complete mesh control that automatically releases during deployment of the reflector. It is another object of the present invention to use a mesh management system on a deployable umbrella-type reflector which controls the mesh and edge members in the stowed condition in order to assure reliable deployment of the reflector in space.
These and other objects and purposes of the present invention will become apparent from the following description of the invention, particularly when viewed in accordance with the accompanying drawings and appended claims.
The present invention provides unique methods, apparatuses, and systems for mesh integration and tension control, mesh retention, and mesh management of a mesh-type reflector. Any deployable mesh-type reflector can benefit from the present invention. In particular, current and future Geo-mobile communication satellites can use the invention in place of mesh reflectors utilizing known art and save expense and weight while enhancing performance and reliability. Other deployable reflectors may also be able to use certain features and aspects of the present invention.
When the mesh reflector is being made, gore-size tensioning tables are used to establish the requisite tension in the gores. Double-sided adhesive tape is used to temporarily lock in the pre-tensions in the gores on the tensioning table until the gores are sewn together. String-like chord members positioned in sewn-over pockets at the outer edges of the gores serve as the catenary members. Once the gores are sewn together forming the flexible mesh reflector member, the pre-tensioned mesh member is positioned on a reflector framework made of a plurality of ribs arranged around a center hub in an elliptical or circular pattern. The mesh reflector is then secured to, and tensioned on, the reflector frame structure. The reflecting surface shape is approximated by many substantially flat trapezoidal facets whose corners or nodes are positioned near attachment points on the frame structure. The edges of the facets are retained in a substantially straight condition by a network of tensioned edge members positioned toward the focus side of the dish-shaped mesh reflector.
Small nodal assemblies with composite bending springs are positioned on each of the corners or nodes of the facets forming the mesh reflecting surface. The assemblies are attached to the framework structure through the mesh and include small xe2x80x9comegaxe2x80x9d-shaped springs. Adjacent pairs of the spring members are alternately oriented in the radial and tangential directions at the nodal assemblies to permit desired tensioning in both radial and tangential edge members. Light thermally stable chord members form the edge members constituting the retention network. Each chord member has one end attached to a bending spring and the other end attached to an adjacent nodal assembly, preferably using an unique adjustable knot mechanism.
Once all of the nodal assemblies and chord members are positioned in place, each chord member is tensioned to a specified value selected to minimize mesh pillowing and tangential loading on the reflector ribs. Compared to prior mesh assemblies which utilize straps tensioned by springs located behind the mesh, the chord member and nodal assembly system is lighter, less expensive, provides less solar blockage, and is easier to accurately tension.
The mesh management system in accordance with the present invention maintains the reflector mesh under tension control during ground handling, launch, and boom deployments, and then automatically releases the tension as the reflector is deployed into its final shape and position. The mesh management system utilizes a framework of chord members, small pieces of tubing, guide washers, beads, and a pair of comb-like rack members. The guide washers are attached to the non-focus side of the mesh reflector member and chord tensioning members are positioned through the washers from the central hub of the reflector to the outer edges of the gores. A single chord member is used near the hub of the reflector and is spliced into two pieces as it approaches the outer edges of the gores. The inner ends of the mesh management chord members are secured to the reflector hub while loops formed at the outer ends are individually slipped over teeth or fingers of the comb-like rack members. The rack members in turn are pivotally secured to the main reflector rib member. Small flexible tubular members are positioned over the mesh management chords adjacent the outer edges of the reflector and beads or similar structures are positioned on the tubular members and used to help hold the mesh into a certain configuration for stowing and launch.
With the mesh management system, the chord members force the majority of the gore material inwardly when the reflector is collapsed and stowed. Near the outer edges of the mesh, however, the management system with the chord members and beaded tubular members urge the outer portions of the mesh upwardly toward the hub or center of the reflector. When the reflector is stowed, loops at the ends of the mesh management chord members are secured to the rack members and the comb teeth are retained in a certain orientation prohibiting release of the chord members. When final deployment commences, the rack members are allowed to rotate allowing the loops to slide off freeing the chord members and tubular members.
With the present invention, initial constraint and final release of the comb-like rack members is achieved without the need for an active release system or separate ground commands. The present invention provides mesh control at less expense and weight and is more reliable than known systems. The present invention requires fewer elements and control steps in order to disengage the stowed mesh and free it at time of deployment.
The above and additional elements, features, benefits and advantages of the present invention will become apparent from the following description of the present invention, particularly when viewed in accordance with the attached claims and accompanying drawings.